2x12 Dura-Ace / Ultegra / 105 / GRX bike won't charge

2x12-speed road and gravel bikes are charged through a charging port located on the rear derailleur.

This works well, until it doesn't. Sometimes these bikes will still shift and respond to the mobile app, but when you connect the charger to the rear derailleur, nothing happens. No LED activity, no charging, nothing.

Don't panic, because in most cases there is an easy fix - clean the charging port / terminal with a bit of alcohol. I tend to use 95%+ myself.

Put the alcohol on a piece of cloth and clean the terminal. Just a quick wipe should do the trick.

Even when the terminal does not appear to be dirty, this is what has always worked for me in the past.